A long standing question in the field of vector biology is how pathogens gain access from the midgut of an insect vector to other organs in the hemocoel, bypassing cellular and non-cellular barriers as well as host defense mechanisms. Although different pathogens may have devised alternative methods to reach other tissues, all are faced with the same barriers. We propose to characterize a growth factor signaling mechanism used by an insect pathogen that can be applicable to pathogens such as malaria parasites and vector-borne viruses. Fibroblast growth factors (FGFs) are a large family of polypeptide growth factors widespread in multicellular organisms and are key regulators in cell differentiation, cell proliferation, and cell motility. In Drosophila, a single fgf, branchless, regulates tracheal cell motility, determining the pattern of its branches. Baculoviruses are large DNA-containing viruses that, similar to other eukaryotic viruses, encode genes that affect the development of their host. Most baculoviruses encode an fgf homolog, vfgf, with similar biochemical properties to the cellular homologs, however, the role of vfgf during virus infection is unknown. The specific mechanism used by baculoviruses to spread infection beyond the primary site of infection, midgut epithelial cells, has not been defined in detail, but tracheolar cells have been implicated as conduits for virus propagation beyond the midgut. We hypothesize that the virus utilizes vfgf to stimulate motility of uninfected tracheolar cells to spread infection systemically. We will characterize a vfgf-knockout baculovirus in insect hosts. Specifically, (1) the infectivity and virulence of vfgf- knockout and vfgf-overexpressing viruses will be determined using 4 insect species at different developmental stages; and (2) we will determine the mechanisms by which baculoviruses traverse the midgut barrier by examining the effect of vFGF on motility and morphology of tracheolar cells servicing the midgut using scanning confocal and transmission electron microscopy. We expect that our results will contribute valuable information to pathogen-vector interactions and pathogenesis. Many insect-vectored pathogens carry human and animal diseases. The specific mechanisms of how the pathogens travel from the insect midgut to the other tissues enabling their transmission are not known. The proposed studies will determine the mechanism used by an insect pathogen to move through its host, develop tools to study other insect pathogens, and in the long run, lead to the development of new strategies to control human pathogen transmission. [unreadable] [unreadable] [unreadable]